Tubulars used to drill and complete wells are typically joined by threaded connections. The most widely used connections, in casings and tubing, have tapered threads without shoulders. Pipe connections depend upon sufficient torque to seal and secure the pipe sections in series. The couplings are of somewhat larger diameter than the joined pipe ends and have tapered box threads to receive the tapered, threaded, ends of the joined pipe sections. The threaded pipe ends are called pins.
Common surface piping connectors are usually called collars but collars in the well drilling industry are the heavy, thick walled, pipe situated near the bit that provides ballast weight to load a drill bit. The term “couplings” will be used herein to define the short tube that joins two sections of pipe.
Well bores are seldom straight. They often jog laterally, to some degree, quite often. Pipe is normally straight relative to well bores and moving a straight pipe through less than straight well bores takes some force. Well bores are usually sized for the pipe to move along the well bores with manageable forces. Very often, the pipe strings have some cutting structure at the lower end. To negotiate a jog in the well bore they are often rotated to ease the downward movement, cutting some formation as necessary. That rotation will often take more torque than the specification torque for the connection process. That excess torque may further drive the pin threads into the couplings. There is a need to allow the couplings to accept more torque without further running of the threads.
The most widely used pipe connections probably are the American Petroleum Institute (API) standard 8-round (LTC or STC) connections and the industry standard coupled buttress (BTC) connections. The related couplings have threads that advance into the coupling from both ends and meet in the middle of the coupling with little or no smooth cylindrical bore remaining.
Pipe strings extending into wells that have considerable deviation from vertical are often rotated, with or without cutting structure on the lower end, as they are lowered into wells to enhance the movement into the wells.
The torque required to rotate the pipe when many sections are assembled may exceed the acceptable torque involved in assembling the pipe string connections. In such cases, again, the threads may advance farther into the couplings, often to a destructive extent. Recently, more casing strings are fitted with cutting structure at the lower end to power through bridges and to deepen drilled wells.
Recently, well drilling is involving more use of the Casing Drilling System (CDS) in which usable rotating torque is reflected in well cost reduction. A rather large part of the well may be drilled with the casing string carrying a drill head, or equivalent. The cost reduction may diminish if shouldered pipe connections have to be used to carry the increased torque.
Pipe strings are often constructed with shoulders. Such shoulders abut and cause a sharp rise in the torque required to further advance the threads. Such shouldered connections may take the pipe string rotating torque and avoid damage to the connections. Such shouldered pipe connections increase the cost of a pipe string.
There is a need to enhance the ability of tapered shoulderless threads to accept increased torque without consequent damage. With an increase in the ability of shoulderless connections to accept pipe rotating torque many more wells can be completed with the more economical, and simpler, threaded arrangements, without shoulders.
It is desirable to extend the usefulness of the more economical pipe connections by using a shouldering ring that allows the ends of the tapered threaded pipe sections to engage a shoulder to prevent pipe rotating torque from overloading the threads in both boxes and pins.
The center of the coupling, between pipe ends, has been defined as the J-space. The diminishing threads in the center of the coupling can be used to confine a floating shoulder ring. The shoulder ring needs to remain in place during handling of the pipe but should be able to float when two pipe ends shorten the J-space during thread make-up.
A short ring having an inner diameter approximating the pipe bore and an outer diameter approximating the radial dimension available in the coupling can engage both ends of pipe entering the coupling boxes and accept axial thrust that the make-up of the connection produces. Excess torque that would damage the threads is accepted by the floating ring and reduces the stress that would otherwise distort the threads and related boxes and pins. The ring can provide sealing abutments, against the pipe ends, that can enhance the differential pressure acceptable by the connection. This invention addresses that objective.
A pipe section normally has one coupling, ideally bucked to specification, before it is introduced to the pipe string assembly area which is normally at the rotary table. It is also desirable to have the floating torque ring installed before it is introduced to the assembly area. The torque ring needs the ability to stay in place during the pipe handling. There is often shock to the pipe section while it is prepared for assembly in the pipe string. This invention addresses that objective.
The torque rings can be held in place by threads on their outer surface that mate with the threads in the coupling. The threads approaching the center of the coupling, from both ends, are of the same pitch and lay. When they meet in the middle, however, they are not normally in axial registry. The threads on the ring, then, need to engage only the threads proceeding from the coupling end receiving the ring.
The ring axial center should be quite close to the axial center of the coupling, considering the tolerances involved. On the eight thread standard, about seven total threads should be exposed between the pipe ends of the assembled connection. Almost four threads of the ring entry end of the coupling should be exposed beyond the end of the pipe when assembly is complete. Two complete threads on the end of the ring toward the open end of the coupling could secure the ring during handling. The number of exposed threads may vary for different sizes of pipe involved.
When the pipe sections are delivered to the rig site, the couplings are usually bucked on to a pipe section to specifications. If so, the couplings would not turn farther on to the mated pipe section when the final pipe section is torqued to specification at the rig. Unfortunately, that is not always the case. Some couplings may turn farther onto their mated pipe thread when the last pipe section is properly connected. Such events would push the installed ring axially. The ring, if it is already bound between the pin ends might not back away along the engaged coupling threads. The threads might be forced and cause damage of unpredictable consequence. There is a need for the threads to yield axially without damage. When the second pipe section is inserted into the box of the coupling, the threads on the ring no longer need to function. The threads can be of such construction that they can hold the ring in place as required until loaded, then fail harmlessly. Failing harmlessly means that the connection is not compromised by the failure of the threads on the sleeve. This invention addresses that problem.
If conditions change and the couplings no longer run farther onto the pipe string when the last pipe section is properly made up into the coupling there will be no need for threads on the ring that harmlessly yield axially. Normal thread forms can be used. That condition is anticipated by, and is within the scope of the claims.
When shoulderless pipe connections are assembled to specification the axial space between the pipe ends has substantial variance due to allowed tolerances. The floating shoulder ring can be supplied in a number of different lengths such that a measurement of the mating parts awaiting assembly can suggest an ideal length to select from the varieties on hand.
The shoulder ring with shallow, well rounded, threads has been bench tested in the worst expectable situation, after both pin ends have engaged the ring and the coupling runs farther onto the originally installed pipe section. The shallow, rounded, threads on the ring were heard to slip a thread. After removing the last pin installed, the ring could be easily removed by hand, with some backward rotation of the ring. The slip of the ring past one, or more, thread qualified as a harmless failure of the thread on the ring.
In some cases, depending somewhat upon the size of the pipe involved, the ring tends to swage radially inward when sufficient axial loads are imposed by the pin being rotated into the coupling. In such cases, the end, or ends, of the ring can be shaped slightly conical and opening outward to prevent the distortion of the ring. That is anticipated by and is inherent in the claims.